MS25-P03 X-ray Absorption Spectroscopy options for crystallographic research at BESSY II Daniel Többens (Department Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Berlin, Germany) Götz Schuck (Department Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Berlin, Germany) Ivo Zizak (Department Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Berlin, Germany) Susan Schorr (Department Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Berlin, Germany)email: daniel.toebbens@helmholtz-berlin.deX-ray absorption spectroscopy (XAS) is increasingly used to study crystallographic problems in a wide range of scientific fields. Its element specificity and sensitivity to the local structure provide high complementarity to X-ray diffraction. Due to the need for radiation with tunable energy it is yet restricted to synchrotron sources. The Berlin Electron Synchrotron BESSY II operates multiple XAS stations for user service, some of which are particularly optimized for crystallographic problems:   

mySpot [1] is optimized for mapping experiments with focus spot sizes as low as 1.5 µm. µ-EXAFS and µ-XANES in the energy range 5 - 25 keV can be combined simultaneously with small or wide angle scattering (SAXS & WAXS),  X-ray fluorescence analysis (XRF), and Raman Scattering.   Lateral focusing lenses with long focal length of 4-7 mm allows scanning of areas and volumes. The experiment is especially designed (but not limited to) for the study of hierarchically structured biological samples.

CryoEXAFS at KMC-3 beamline, developed in cooperation with Freie Universität Berlin [3], allows sample temperatures as low as 20 K, with convenient sample change at cold temperatures. Due to the absence of absorption in air, low radiation energies (3.6 - 14 keV) can be used, extending the range of observable light elements. 

KMC-2 XANES [3] provides a stable beam in the energy range 4 – 15 keV, microfocus option and a selection of detectors, allowing transmission and fluorescence geometries. The open concept of the station allows the use of a wide range of sample environments, both in-house and user-provided, and flexible movement of the sample. A particular strong point is the suit of atmosphere control systems [4], which allows for continuous flow or volumetric control, high and low temperatures and pressures, precarious gases and, added most recently, humidity control.
 
References:

[1] Helmholtz-Zentrum Berlin für Materialien und Energie. (2016). mySpot: a versatile microfocussing station for scanning methods at BESSY II. Journal of large-scale research facilities, 2, A101. doi 10.17815/jlsrf-2-115

[2] Helmholtz-Zentrum Berlin für Materialien und Energie. (2016). KMC-2: an X-ray beamline with dedicated diffraction and XAS endstations at BESSY II. Journal of large-scale research facilities, 2, A49. doi 10.17815/jlsrf-2-65

[3] H. Dau, Institut für Experimentalphysik, Freie Universität Berlin

[4] Sample Environment available at BESSY-II, https://www.helmholtz-berlin.de/user/experimental-infrastructures/sample-environment/se-at-bessy/specifications_en.html

Keywords: EXAFS, XAS, Synchrotron